Zinc oxide thin film-based MEMS acoustic sensor with tunnel for pressure compensation

An acoustic sensor exhibiting enhanced sensitivity has been fabricated after integrating the piezoelectric zinc oxide (ZnO) thin film with silicon micro-electro-mechanical system (MEMS) having pressure compensation tunnel. The sensor structure comprises of silicon diaphragm loaded with a layered structure where a highly c-axis oriented ZnO thin film (3 μm thick) fabricated by RF magnetron sputtering, has been sandwiched between PECVD deposited SiO2 layers. The pressure compensation in the developed acoustic sensor is achieved using a tunnel in the MEMS structure. The response characteristics of the acoustic sensors are reproducible for the devices prepared under similar processing conditions under different batches. The measured value of central capacitance and dissipation factor of the sensor is about 65 pF and 0.003, respectively, whereas the value of ∼144 pF is obtained for the rim capacitance with a dissipation factor of 0.005. The sensor was found to exhibit enhanced sensitivity of about 300 μV/Pa (rms) under varying acoustic pressure and can be used effectively over a wide frequency range (30 Hz to 8 kHz).